Switched power conversion results in electromagnetic interferences (EMI). To prevent the power conversion from disturbing other electronic equipment, certain requirements for maximum allowed interference levels have to be met. These interferences are measured over a frequency interval. One solution to reduce the interferences to allowable levels is to use filters. Another solution is to spread the energy of the interference over a broad frequency interval, through frequency modulation of the switching frequency. Such a solution is known from U.S. Pat. No. 4,190,882.
The problem with the first solution is that filter components tends to be large and heavy. The problem with the second solution is that, although the amplitude of the spread-out switching frequency band is substantially decreased, the frequency modulated switching still runs the risk of disturbing the function to which the converted power is intended to be used, e.g. a radar function if the modulation frequency is transferred further in the radar system. A radar is intended to discover electromagnetic radiation, and due to the Doppler effect, it is not known which frequency a received signal will have if you have moving objects within the coverage of the radar. The switching frequency or its harmonics or sub harmonics can therefore be mistaken for a moving object.
There is thus a need to accomplish an improved radar system comprising a switching mode power converter, which is not based on large and heavy filter components, and in which the switching frequency or its harmonics or sub harmonics will not be mistaken for a moving object by the radar unit.